It is narrated from Sayyiduna Wa'il bin Hujr (may Allah be pleased with him) that when the Messenger of Allah (peace and blessings be upon him) bowed (in ruku'), he kept his fingers spread apart, and when he prostrated, he kept his fingers together.
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18246